Over the past several decades, scientists have postulated that PPARγ is the generally accepted site of action for insulin sensitizing thiazolidinedione compounds.
Peroxisome Proliferator Activated Receptors (PPARs) are members of the nuclear hormone receptor super-family, which are ligand-activated transcription factors regulating gene expression. PPARs have been implicated in autoimmune diseases and other diseases, i.e., diabetes mellitus, cardiovascular and gastrointestinal disease, and Alzheimer's disease.
PPARγ is a key regulator of adipocyte differentiation and lipid metabolism. PPARγ is also found in other cell types including fibroblasts, myocytes, breast cells, human bone-marrow precursors, and macrophages/monocytes. In addition, PPARγ has been shown in macrophage foam cells in atherosclerotic plaques.
Thiazolidinediones, such as pioglitazone, developed originally for the treatment of type-2 diabetes, generally exhibit high affinity as PPARγ ligands. The finding that thiazolidinediones might mediate their therapeutic effects through direct interactions with PPARγ helped to establish the concept that PPARγ is a key regulator of glucose and lipid homeostasis. However, compounds that involve the activation of PPARγ, such as pioglitazone, also trigger sodium reabsorption and other unpleasant side effects.